book Maths Puzzle Numerical Ability

can you please help me with this question?

y-(y+3)=y+6

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I need help solving this problem: T(x)=Ax, find vector x whose image under T is b. Is x unique?
A=
1 -2 1
3 -4 5
0 1 1
-3 5 -4
b=
1
9
3
-6 Please check my work
Solve using the quadratic equation:
(3x^2-2x) + (-15x+10)=0
(3x^2 - 17x +10)= 0
(3x^2 -2x -15x +10)=0
x(3x-2) + (-5) (3x-2)=0
(x-5)(3x-2)=0
(x-5)=0 or (3x-2)=0
x=5 or 3x=2
x=5 or x=2/3